Performance of a navigation system can be determined by the error distribution in navigation measurements (e.g., accuracy) provided by the system. System performance may also depend on its ability to provide timely warnings to users when it should not be used (e.g., integrity). Performance may also be measured by how long a navigation system takes to achieve its first position fix from a cold start (e.g., time to first fix). In addition, system performance may depend on the fraction of time or particular circumstances in which specified performance parameters fall within specified limits (e.g., availability).
Unfortunately, the navigation signals provided by various existing navigation systems often do not provide satisfactory system performance. In particular, the signal power, bandwidth, and geometrical leverage of such navigation signals are generally insufficient to meet the needs of many demanding usage scenarios.
Existing navigation approaches based, for example, on Global Positioning System (GPS) signals often provide insufficient signal power or geometry to readily penetrate buildings or urban canyons. Such signals may also be susceptible to jamming in hostile environments, and can prevent their usage in safety-of-life applications. Other navigation approaches based, for example, on cellular telephone or television signals typically lack vertical navigation information.